This invention relates to a method for increasing the ore yield and improving the working conditions in mines. More particularly, it relates to a mining method suitable for exploiting seams of coal, salt, potash, trona, oil shale, petroleum, tar sands, uranium, sand and gravel, talc, and the like, and to improvements in the mining method wherein a seam of ore having an overburden is exploited by excavating a series of elongate approximately parallel chambers in the seam.
It is now commonplace to mine seams of valuable minerals having an overburden by the "room and pillar" method. This involves digging out a trench, drift, bench, or tunnel to provide access to an edge of the seam and thereafter sequentially tunneling a series of chambers into the exposed access wall. Depending on the nature of the ore, the tunneling is conducted by workmen equipped with suitable mechanical devices, by a remotely controlled mechanical mole, or by employing mining augers of the type which operate by the same general principle as the carpenter's brace and bit. The latter method is well suited for mining friable ores such as coal, salt, potash, trona, and the like. The most significant drawback of this mining technique is that no inexpensive way has been forthcoming to prevent caving of both the excavated chambers and the ore face (access wall).
U.S. Pat. No. 2,990,166 to M. A. Walsh, entitled Mining Method, the disclosure of which is incorporated herein by reference, discloses one particularly advantageous and inexpensive method of temporarily supporting such chambers. As disclosed in the '166 patent, after a chamber is completed, an inflatable, flexible container or bladder is placed therein and inflated from a remote point such that it contacts at least the floor and ceiling of the chamber and supports the overburden. Since the overburden is supported, the next successive chamber may be excavated fairly closely adjacent the previously excavated chamber, leaving only a thin rib or pillar of material separating the two. After working a safe distance down the face of the access wall, the bladders contained in the chamber remote from the newest excavation are removed and caving is allowed to occur. Alternatively, caving may be induced by increasing and decreasing the pressure in the bladders.
While the foregoing method has many obvious advantages, it provides only temporary support, and removal of the bladders frequently results not only in caving of the chambers but also of the access wall. Usually, the access tunnel or trench must be maintained free of gob and in a structurally sound condition. Also, for reasons of safety and efficient utilization of conveying and mining equipment, it is frequently necessary to plug the openings between the access tunnel and the chambers to control flooding and the flow of noxious gases emanating from the excavated chambers. For these reasons, the access wall must often be permanently supported, for example, by being furnished with a suitable masonary structure located in the mouth of the opening. Obviously, this is a costly procedure and presents a potential hazard to the workmen building the structure.